Nick Hawkins, a naturalist guide with a tour boat operation based in Passamaquoddy Bay, said Friday he has seen sharks in the bay before.

Monday’s sighting of a great white shark, just outside the harbor of St. Andrews, New Brunswick, where the tour company Quoddy Link Marine is based, was not even his first sighting of that species, considered to be one of the top predators in the ocean. St. Andrews is just across the border in Canada, about 3 miles from Robbinston, Maine.

Hawkins said this summer is the fifth in a row he has worked as a naturalist with the tour company. In 2012, he said, he and others on a tour in the bay caught a brief glimpse off the boat’s stern of a great white attacking and eating a porpoise.

Monday’s sighting was a more drawn-out affair, he said, which gave passengers the opportunity to take photographs and record video of the shark as it idly swam alongside the boat. Hawkins said the shark casually turned away from the boat several times, but the boat followed it each time. The encounter lasted about 10 minutes before the shark finally swam away.

“Four or five times, we had it directly alongside the boat,” Hawkins said. “You could have jumped right onto its back.”

He said he and the captain of the boat estimated the shark to be about 15 feet long, a size considered to be a fully mature great white.

Hawkins said there “have always been” seasonal sightings of sharks off Canada’s maritime provinces, but there is a consensus they are becoming a more common sight farther north in the summer, when mild surface water temperatures expand their range.

“The prevalence of sharks is on the rise,” he said.

According to federal officials in the United States, a scientific study released in June indicates the number of great white sharks off the East Coast is increasing.

The population of great whites decreased in the 1970s and ’80s, most likely because of commercial and recreational shark fishing, but has expanded since the 1990s, when federal restrictions were placed on shark fishing and the harvesting of great whites specifically was banned, officials with the Northeast Fisheries Science Center have said.

It’s not the first time there has been a shark encounter in the area. In 2010, a diver avoided injury when he used an underwater video camera to fight off an attack from a porbeagle shark in Broad Cove off Eastport. Other types of sharks that have been seen off Maine’s coast over the years include basking, sand, tiger, mako, thresher, blue sharks and the ubiquitous dogfish.

Warren Joyce, a shark technician with the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, said Friday in an email that, based on photos and video of the St. Andrews sighting, shark experts in Canada believe it was a great white.

Joyce said there is some evidence the populations of some shark species may be growing in the coastal waters of the Northeast.

“Some of the factors contributing to that rise would be a decrease in commercial fishing (our directed porbeagle fishery in Canada has recently been closed), protection of known mating and pupping grounds, and an increase in food,” Joyce said. “There are large marine mammal and seal populations in the Gulf of Maine/Bay of Fundy areas, which are the main diet of large white sharks.”

But, Joyce added, an increase in the amount of boat traffic along the Canadian and U.S. shores in the North Atlantic also may be a factor in the number of sightings.

“There is still a lot we do not know about many of the shark species in our waters, but I believe that, to be sure of an increase, more study and monitoring is necessary,” he said.